The professional amplification and sound recording sector is well aware that in order to reach acceptable quality in the reproduction of a musical event such as musical instruments and/or microphones, either using a pre-recorded program or amplifying live the sound source, the reproduction system of amplification or sound recording must reproduce a wide range of frequencies, from very low (30 Hz, for example) to the highest pitch (15000 Hz for example) in a balanced way and with sufficient distribution of energy.
Furthermore, this system must be able to reproduce this wide band at the required level, without harmful distortion for those listening to the musical event. In order to achieve high levels capable of covering wide areas with a large public, very high power together with adequate transducer efficiency is necessary, especially and above all at low frequencies.
Therefore, the speaker which has the task of reproducing the sound range having low frequencies must be equipped with a speaker or speakers suitable for supporting high pilot voltage besides having high transducer efficiency, achieved thanks to a large diameter diaphragm and/or a very high peak to peak excursion capacity of the same, or also thanks to a sound reproducer, like the horn, which acting as a true impedance transformer in relation to the means of propagation, the surrounding air, increases its efficiency because of its more favorable adaptation to sound.
In any case, however, a speaker like this, performing well at low frequencies, in particular if it has a horn sound reproducer, is large and takes up a lot of space. The larger the horn for low frequency is, the larger the phase inverter and band-pass “cabinet”, made according to the principle of recovery of rear emission of the speaker, will be. In the same way the larger the classical and simple closed “cabinet” operating according to the principle of pneumatic suspension is, the lower the frequencies reproduced and the higher the sound energy produced in the surrounding space will be.
Therefore, in order to reproduce these frequencies it is usual to use separate and dedicated speakers called “subwoofers”, because they are used to reproduce lower frequencies than the “woofer” which usually house one or more specialized speakers in “cabinets” varying in size from 100 to 300 dm3 (litres) of overall volume to well over this figure, which are very large or anyway by no means easy to manage.
The latter characteristic, necessary to achieve high low frequency efficiency, if on the one hand hardly impairs the result in terms of loss of space in the fixed type of installation, it does on the other hand negatively impair the type designed to be portable where, because of economic reasons and running costs, the means of transport of the necessary materials is only just the right size or even slightly too small.
This often results in the use of “reduced band” transportable sound systems both for pre-recorded and live music, where the reproduction of the low frequency range, entrusted to the aforesaid “subwoofer”, is almost completely lacking, with serious impairment of the musicality and the impact that this specific speaker makes on the musical event.
In other words, for those using portable amplification systems, such as small bands or small rent-out services who have limited available space because of the few and small means of transport they have at their disposition, bearing also in mind the growing costs of purchasing and running larger vehicles, the sound reproduced is very often penalized because of these people deciding not to use one or more special low frequency speakers in addition to the necessary wide band speakers, the so called satellites, which are usually much smaller.